In recent years, an amount of information processing required for a digital electronic device is continuously increasing, and accordingly, the signal speed in the digital electronic device is speeded up. Consequently, many simulations performed in the product design phase correspond to high-speed signals.
One of the functions of a simulator that performs such a simulation includes a function of displaying a signal waveform analysis result in an eye pattern. And, it is needed to construct a technique for quantitative evaluation of the eye pattern.
A simulator generates an eye pattern by superimposing waveform signal pieces in a specified length that are sequentially cut out from waveform signals generated by the simulator. For example, a pattern shape as illustrated in FIG. 18 is expressed when waveform signal pieces with a length of two clock cycles are sequentially cut out and superimposed.
A maker that provides a receiving device presents a mask in a shape as illustrated for example in FIG. 19A to 19C as a specification of the receiving device. And then, the maker requests that the mask falls within the opening of the eye pattern when the receiving device is used.
As illustrated in FIG. 19A, the shape of the mask illustrated in FIG. 19A to 19C can be specified by designating α (time value), β (time value), and γ (voltage value). As a result, the center location of the mask is designated as illustrated in FIG. 19B. And, mask locations (time coordinate values and voltage coordinate values) of feature points such as point r, point s, point t, point u, point p, and point q included in the mask are designated as illustrated in FIG. 19C.
When the mask is presented, the designer of the maker who uses the receiving device generates waveform signals to be received by the receiving device by the simulator. And, the designer sequentially cuts out waveform signal pieces with a specified length from the waveform signals, and superimposes the waveform signal pieces to generate an eye pattern, in the design phase. And then, the designer checks whether the mask falls within an opening of the generated eye pattern, and, when the mask does not fall within the opening, changes the design of the operating frequency, transmission path, and the like so that the mask falls within the opening.
To perform the check, conventionally, the generated eye pattern is displayed on a display, and the mask relative to the eye pattern is displayed on the display in a format that the mask can move in the time axis direction. The designer moves the mask to a time location where the margin is expected to be the largest, and at the time location, visually measures a margin (margin included in the eye pattern relative to the mask) defined by a distance between the eye pattern and the mask.
However, when such a conventional technique is followed, the user as a designer needs to adjust the location of the mask. Therefore, there is a problem that a great burden is imposed on the user, and there is a problem that variations in margin measurements are large due to differences in the users.
Under the circumstances, one of us proposed a technique in Patent Document 1 listed below. The technique is as follow. A plot inside an eye pattern is created to allow automatic measurement of a margin relative to a mask. And, the mask is moved in a certain direction of the time axis by arbitrary steps to obtain the margin in each destination. A mask location immediately before a difference value of margin relative to adjacent destinations turns from positive to negative is determined to be optimal, and the margin at that point is determined as a final margin.
Patent Document 2 listed below describes a technique concerning a transmitting apparatus that automatically measures a discrimination point with the least occurrence of error in an effective area of an eye pattern and treats the discrimination point as an optimal point to control the reproduction.
Patent Document 3 listed below describes a technique concerning a bit synchronizing circuit that extracts a center phase of an eye opening part without depending on the jitter distribution of input data to secure an optimal retiming margin.
Patent Document 1 Japanese Laid-Open Patent Publication No. 2006-90788
Patent Document 2 Japanese Laid-Open Patent Publication No. 2003-18140
Patent Document 3 Japanese Laid-Open Patent Publication No. 2000-332736
In the conventional techniques, to measure a margin between an eye pattern generated by a simulator and a mask, the generated eye pattern is displayed on a display, and the mask relative to the eye pattern is displayed on the display in a format that the mask can be moved in the time axis direction. The designer moves the mask to a time location where the margin is expected to be the largest, and at the time location, visually measures a margin between the eye pattern and the mask.
However, when such conventional techniques are followed, the user as a designer needs to adjust the location of the mask. Therefore, there is a problem that a great burden is imposed on the user, and there is a problem that variations in margin measurements are large due to differences in the users.
Under the circumstances, one of us disclosed the technique in Patent Document 1. That is, the plot inside an eye pattern is created to allow automatic measurement of the margin relative to a mask. And, the mask is moved in the certain direction of the time axis by arbitrary steps to obtain the margin in each destination. The mask location immediately before the difference value of margin relative to adjacent destinations turns from positive to negative is determined to be optimal, and the margin at that time is determined as the final margin.
However, the optimal mask location obtained in the invention may not be a mask location required when the receiving device actually operates. Therefore, there is a problem that it cannot be stated that the margin obtained in the invention always indicates an accurate margin.
The techniques described in Patent Documents 2 and 3 are techniques made to improve an actual operating state of the receiving device and are not inventions for realizing an automatic evaluation of the size of the opening of the eye pattern generated by the simulator.